ISLAMABAD, Pakistan — The assassination of an outspoken secular politician by one of his elite police guards on Tuesday plunged the government deeper into political crisis and highlighted the threat of militant infiltration even within the nation’s security forces.

The killing of Salman Taseer, the prominent governor of Punjab Province, was another grim reminder of the risks that Pakistani leaders take to oppose religious extremists, at a time when the United States is pushing Pakistan for greater cooperation in the war in Afghanistan by cracking down on militant groups like the Taliban.

Mr. Taseer, 65, a successful businessman and publisher of a liberal English-language daily newspaper, was exceptional, even within the secular-minded Pakistan Peoples Party, for his vocal opposition to the religious parties and the extremism they spread. He was imprisoned in the 1980s under the military dictator Gen. Mohammad Zia ul-Haq for it and was still opposing the religious parties 30 years later.

He recently took up a campaign to repeal Pakistan’s contentious blasphemy laws, which were passed under General Zia as a way to promote Islam and unite the country. The laws have been misused to convict minority Pakistanis as the Islamic forces unleashed by the general have gathered strength. The laws prescribe a mandatory death sentence for anyone convicted of insulting Islam.

Religious parties staged vigorous demonstrations of thousands of people across the country last weekend to protest the campaign by Mr. Taseer, even burning him in effigy. Mr. Taseer countered in comments on his Twitter account and elsewhere.

“Religous right trying 2 pressurise from the street their support of blasphemy laws. Point is it must be decided in Parlaiment not on the road,” he wrote on Dec. 26 in the imperfect shorthand typical of such posts.

Photo

Malik Mumtaz Hussain Qadri, center, a security guard, is being held in the killing of Salman Taseer, governor of Punjab Province.Credit
Tariq Waseem/Associated Press

“I was under huge pressure sure 2 cow down b4 rightest pressure on blasphemy. Refused. Even if I’m the last man standing,” he posted on Dec. 31.

On Tuesday Mr. Taseer was shot in daylight multiple times at close range as he was getting into his car in Islamabad at the Kohsar Market, an area frequently visited by the city’s elite. His attacker was identified as Malik Mumtaz Hussain Qadri, an elite-force security guard, who surrendered to the police immediately afterward and implied he had killed the governor because of his campaign to amend the blasphemy laws.

“I am a slave of the Prophet, and the punishment for one who commits blasphemy is death,” he told a television crew from Dunya TV that arrived at the scene shortly after the killing, according to Nasim Zahra, the director of news at the channel.

It was not yet clear whether he had acted alone or on behalf of some extremist group.

Mr. Taseer’s death will serve as a chilling warning to any politician who speaks out against the religious parties and their agenda and will certainly end immediate attempts to amend the blasphemy laws, politicians said. “It is a loss to progressive forces; he stood up for what he believed in,” said one of his party colleagues, Sherry Rehman, a legislator.

Yet Ms. Rehman, who has long worked to amend the blasphemy laws, said the party should regroup and continue to pursue the issue because it is central to the liberal politics that the Pakistan Peoples Party and Mr. Taseer have stood for.

“You can recoil in fear, or you can have a considered action and regroup sensibly at a time when it is approachable and applicable,” she said.

Like Mr. Taseer, Ms. Rehman has frequently received threats, but she said the future of the country was at stake. “You have to understand the gravity of the challenge,” she said. “Personal safety is at risk, but there is also an existential threat to Pakistan.”

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Police officers in Islamabad, Pakistan, collected evidence at the scene where Salman Taseer, the governor of Punjab province, was shot dead by one of his guards on Tuesday.Credit
Muhammed Muheisen/Associated Press

Mr. Taseer’s death will also be a severe loss for the governing Pakistan Peoples Party and President Asif Ali Zardari; Mr. Taseer was the president’s personal friend and close political ally. As governor of Punjab, the nation’s populous heartland, he was a bulwark against spreading radicalism and the main opposition party, the Pakistan Muslim League-N, led by Nawaz Sharif and his brother Shahbaz.

On Tuesday, the Sharifs’ party added to the national government’s troubles, giving the Pakistan Peoples Party a three-day deadline, extended for three more days in the wake of the assassination, to accept a list of demands to avert a no-confidence vote. These included a reversal of recent fuel price increases, cuts in spending of 30 percent and the enforcement of a series of court verdicts against governing party officials for corruption.

Obama administration officials worry that even if Pakistan’s government survives the upheaval — which they believe it might, for a while — the turmoil could kill any chance for political and economic reforms. The assassination, one official said, leaves not only the repeal of the blasphemy laws in doubt, but also possible reforms to increase tax collection. Under pressure from Secretary of State Hillary Rodham Clinton and other American officials, the Pakistani government submitted a new tax law in Parliament. But it may abandon the push as a way to lure back coalition partners.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said in an interview on Tuesday that he was “hugely concerned” when he learned of the assassination, but that he expected Pakistan and its security relations with the United States to weather the crisis.

Members of the Pakistan Peoples Party were shaken to the core by the killing, which occurred within days of the anniversary of the assassination of former Prime Minister Benazir Bhutto three years ago. The killing also resurrected the party’s fears of the extensive infiltration of extremists in the government institutions, like the military and the police, of the nuclear-armed country.

President Zardari, Ms. Bhutto’s husband, has blamed police and intelligence officials for her death, and his senior aides blamed infiltration of the elite Punjab security force for the governor’s death.

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Salman Taseer pictured in May 2008 laying flowers at the grave of Benazir Bhutto.Credit
Reuters

“It was well organized; it was a jihadi element in the force that was there to protect him,” said a presidential spokeswoman, Farahnaz Ispahani, who spoke tearfully about Mr. Taseer’s death on the Express TV news channel Tuesday night.

Ms. Ispahani invoked the legacy of Pakistan’s secular founder, Muhammad Ali Jinnah, using the popular title for him, Great Leader: “Show me another party where the leaders are being murdered, and why is that? Because we are standing up for Quaid-i-Azam’s Pakistan, and against extremism and terrorism.”

Hundreds of party members and friends gathered at Mr. Taseer’s home in Lahore as his body was taken back from the capital on Tuesday evening, said Ahmed Rashid, an author and journalist. While many mourned a friend, Mr. Taseer’s supporters warned that Pakistan had lost, after Ms. Bhutto, probably the most outspoken and determined advocate against religious extremism in the country.

While the liberal and progressive segments of society saw Mr. Taseer as a courageous and admirable leader, he was loathed by the extreme right. An indication of this disdain was evident in post-assassination statements by most religious leaders, who were reluctant to condemn the killing.

Citing hospital officials, local news media reports said that Mr. Taseer had been struck by nine bullets. But hospital officials later said that 24 bullets had hit him.

President Zardari expressed shock at the assassination, and a statement from the prime minister’s office announced a three-day state of mourning. The funeral will be held in Lahore in the Governor’s House, according to officials and party members.

Rehman Malik, the interior minister, told reporters that an investigation had been started to determine the motives of the assassin and whether he had acted alone.

Mr. Malik was quoted by the Geo Television network as saying that the killer had volunteered to be on Mr. Taseer’s security detail on Tuesday morning. Mr. Malik said the Punjab police official who enlisted Mr. Qadri on the security detail had been taken in for questioning.

Correction: January 7, 2011

An article on Wednesday about the assassination of Salman Taseer, an outspoken secular politician in Pakistan, misstated the decade in which he was imprisoned by the military dictator Gen. Mohammad Zia ul-Haq for his opposition to the rise of religious parties and the extremism they spread. It was the 1980s, not the 1970s.

A version of this article appears in print on January 5, 2011, on Page A1 of the New York edition with the headline: POLITICAL KILLING ADDS TO TURMOIL WITHIN PAKISTAN. Order Reprints|Today's Paper|Subscribe